Question

在插入＆＃39;年之前我需要检查一下。（学术报告）栏目，它不低于报名日期＆＃39; （学生）栏目

我的桌子：

CREATE TABLE STUDENT
(
 BCN INT (10) ,
 Enrollment_Date timestamp not null default CURRENT_TIMESTAMP, 
 primary key (BCN),          
);


CREATE TABLE ACADEMIC_REPORT
( 
    Stud_Num INT(10) ,
    Year year ,
    primary key (Stud_Num , Year ),

    foreign key (Stud_Num ) references STUDENT( BCN )
    ON DELETE restrict       ON UPDATE CASCADE
);

我试过这个：

    /* ACADEMIC_REPORT._Year Constraint "BEFORE INSERT" */
delimiter //    
CREATE TRIGGER ReportYearBIN BEFORE INSERT ON  ACADEMIC_REPORT
FOR EACH ROW
BEGIN
   declare  num  int(10);
   SET num= (SELECT BCN
             FROM STUDENT , ACADEMIC_REPORT 
             WHERE BCN = ACADEMIC_REPORT.Stud_Num );

        IF (ACADEMIC_REPORT.Year < YEAR(num.Enrollment_Date))
        THEN
    SIGNAL SQLSTATE '10000'
        SET MESSAGE_TEXT = 'Error....!';
    END IF;
END;
// delimiter ;

但是在插入

期间会导致此错误

Error Code: 1054. Unknown column 'ACADEMIC_REPORT.Year' in 'field list'

我该怎样做这个约束？

使用MySql工作台6.3

提前谢谢。

Answer 1

好的，我为你想要生成错误的条件创建了一个select语句。如果该报告的学生存在并且报告年度小于学生注册日期，则它将为选择查询生成一行或多行。然后，进程FOUND_ROWS（）将大于0，这将触发您的错误消息。

CREATE TRIGGER ReportYearBIN BEFORE INSERT ON  ACADEMIC_REPORT
FOR EACH ROW
BEGIN
   SELECT * FROM STUDENT WHERE BCN=new.Stud_Num AND new._year < Enrollment_Date
   IF (SELECT FOUND_ROWS() > 0)
        THEN
    SIGNAL SQLSTATE '10000'
        SET MESSAGE_TEXT = 'Error....!';
    END IF;

END;

Answer 2

我已经找到了问题：）

这句话完全错了，

 YEAR(num.Enrollment_Date)

因为编写attribute.attribute不正确，所以只能使用Table.Attribute。

所以，这是解决方案

    /* ACADEMIC_REPORT._Year Constraint "BEFORE INSERT" */
delimiter //    
CREATE TRIGGER ReportYearBIN BEFORE INSERT ON  ACADEMIC_REPORT
FOR EACH ROW
BEGIN
   declare Enroll timestamp;
   SET Enroll = (SELECT Enrollment_Date
                 FROM STUDENT 
                 WHERE BCN = new.Stud_Num);

        IF ( new._year < YEAR(Enroll))
        THEN
    SIGNAL SQLSTATE '10000'
        SET MESSAGE_TEXT = 'Error..The Report year cannot be less than the enrollment year..!';
    END IF;
END;
// delimiter ;

比较来自不同表的两个值 - MySql

2 个答案: